Acceleration and Deceleration Lanes

[CPENG78]

Hello All,
I have a project fronting a roadway under Caltrans Jurisdiction. In the existing condition there are small 20 driveways leading a roadway with a 55 mph posted speed limit.

In the proposed condition I will be installing a 52 ft wide entry road to a small development. This road will include two 12 ft lanes, one entry and one exist and large median element in between.

Since this intersection would not be signalized, there would be the need for both an acceleration and deceleration lanes which lengths to be based on Caltrans standards. This was my original approach.

I spoke to someone at Caltrans and they stated that their acceleration and deceleration standards are meant for freeways and not this type of road. Their response is not very helpful as I am trying to do an initial study that addresses the potential issues involved with such development. Falling short of recommending to the owner of hiring a traffic engineer, does anyone outer have any suggestion.

Lengths shown on the attachment are based on the Caltrans design manual. Thank you.

 

[Maury]

I see no need for an acceleration lane. Traffic from the side road will wait for a gap in traffic before entering. The deceleration lane or right turn only lane is a good idea.

 

[ACtrafficengr]

What's the traffic volume on the main road?

If I were to go through all that expense, I'd make it a left turn lane. You'd get much more safety and efficiency for about the same cost as your proposed design - a 33% (urban) to 44% (rural) reduction in crashes, compared to 14% for a right turn lane.

Safety Effectiveness of Intersection Left- and Right-Turn Lanes

http://www.fhwa.dot.gov/publications/research/safety/02103/02103techbrief.pdf

 

[civilman72]

Assuming this road will only serve twenty single-family homes, I doubt that auxilary turn lanes would be necessary or required.

 

[beej67]

I would assume for your 'initial study' that you'll need the decel lane and a short accel taper, but not the full acceleration lane. Then if you don't have to provide it later, you go from zero to hero instead of visa versa if Caltrans suddenly changes their mind.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[fattdad]

I'm with VDOT. This question is not in my division, but I was just working on a job and for 60 mph (posted at 55) the answer was 600 ft. More if you want some length for storage, which for this job was an additional 100 ft. Not sure about the acceleration lane. Do you have sight-distance issues?

f-d

¡papá gordo ain’t no madre flaca!